This is impossible to measure. I would say that the odds of our readers "getting" exactly our reason for a typeface choice is not very high unless the target audience is the design/typography crowd. That does not mean our loves' labours are lost, it just means audiences can't verbalize intangible effects.

Would you think that your choices are based more on the legibility of the typefaces or their expressive qualities? I would presume that for the web our choices are much more limited and detrimental to the readers experience. But is this the case?